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Abstract:

The present, invention relates to a light emitting diode driver that
integrates a light emitting diode control function and a power switching
control function at a secondary side insulated from a primary side in a
power supply circuit, without using a photo coupler to control power
switching at the primary side.

Claims:

1. A light emitting diode driver, comprising: a power supplier including
a primary side and a secondary side electrically insulated from each
other, switching input power at the primary side and converting the
switched power into driving power having a previously set voltage level
at the secondary side, and supplying the driving power to at least one
light emitting diode (LED) channel; a driver controlling a supply and an
interruption of the driving power to the at least one LED channel from
the power supplier to drive the at least one LED channel and controlling
switching of the power supplier according to a state of the driving power
supplied to the at least one LED channel; and a transfer unit
transferring a switching control signal controlling the switching of the
power supplier from the driver to the primary side of the power supplier
from the secondary side thereof.

2. The light emitting diode driver of claim 1, wherein the driver
includes: a switch unit connected between the at least one LED channel
and a ground to switch the supply or interruption of the driving power to
the at least one LED channel; and a controller detecting the state of the
driving power supplied to the at least one LED channel to control the
switching of the switching unit and generating the switching control
signal according to the state of the detected driving power and to
transfer the generated switching control signal to the transfer unit.

3. The light emitting diode driver of claim 2, wherein the controller
includes: a current generator generating current set according to the
state of the detected driving power; a clock generator generating a clock
signal having a period set according to the current generated by the
current generator; a dead time generator generating a dead time of the
clock signal generated by the clock generator according to the current
generated by the current generator; a gate driver processing the clock
signal having the dead time generated by the dead time generator to
control the switching of the power supplier and transferring the
processed clock signal to the transfer unit; a dimming unit controlling
the switching of the switching unit according to the state of the
detected driving power to control luminance of the at least one LED
channel; and a protection unit interrupting an operation of the gate
driver when the state of the detected driving power corresponds to a
previously set abnormal operation.

4. The light emitting diode driver of claim 3, wherein the dimming unit
includes: a calculator receiving the state of the detected driving power
as a detection signal to calculate a current control signal transferred
to the current generator when a pulse width modulation (PWM) signal
turning-on and turning-off the switch unit is a high signal; and a buffer
unit controlling a voltage level of the detection signal to a previously
set voltage level when the PWM signal is a low signal.

5. The light emitting diode driver of claim 1, wherein the transfer unit
is a pulse transformer including a first winding that receives the
switching control signal from the gate driver and a second winding that
is electrically insulated from the first winding and receives the
switching control signal input to the first winding to transfer the
received switching control signal to the power supplier.

6. The light emitting diode driver of claim 1, further comprising a
rectifier rectifying the driving power from the power supplier and
supplying the rectified driving power to the at least one LED channel.

7. The light emitting diode driver of claim 1, wherein the power supplier
supplies the driving power to each of first and second LED channels of at
least one LED channel block having the first and second LED channels.

8. The light emitting diode driver of claim 7, further comprising a
current balance unit having at least, one current balance unit element
that maintains current balance in the driving power supplied to each of
the first and second LED channels.

9. The light emitting diode driver of claim 8, wherein the at least one
current balance unit element, includes: a current balance capacitor
maintaining current balance between the driving power transferred to each
of the first and second LED channels according to a charge balance law;
first and second diodes connected between the first LED channel and a
ground in series to rectify the driving power; third and fourth diodes
connected between the second LED channel and the ground in series to
rectify the driving power; a first stabilization capacitor connected to
the first and second diodes in parallel to stabilize the driving power
supplied to the first LED channel; and a second stabilization capacitor
connected to the third and fourth diodes in parallel to stabilize the
driving power supplied to the second LED channel.

10. The light emitting diode driver of claim 9, wherein the power
supplier includes: a rectifying and smoothing unit rectifying and
smoothing commercial power; a power factor correction unit adjusting a
phase difference between voltage and current of the rectified power from
the rectifying and smoothing unit; a switching unit switching power of
which power factor is corrected from the power factor correction unit
according to the switching control signal; and a transformer having at
least one primary winding that receives the switched power from the
switching unit and at least one secondary winding that is insulated from
the at least one primary winding and receives the power from the at least
one primary winding by forming a previously set turn ratio.

11. The light emitting diode driver of claim 10, wherein the transformer
includes a plurality of secondary windings, the secondary windings
respectively connected to a plurality of LED channel blocks, and
supplying the driving power to a corresponding LED channel block, and the
current balance unit including the current balance unit element provided
in plural to maintain the driving power from the plurality of secondary
windings in a current balance state and supply the current balanced
driving power to the first LED channel and the second LED channel of a
corresponding LED channel block.

12. The light emitting diode driver of claim 10, wherein the transformer
includes a plurality of primary windings respectively corresponding to
the plurality of secondary windings.

13. The light emitting diode driver of claim 1, wherein the power
supplier supplies the driving power to each of first and second LED
channels of at least one LED channel block having the first and second
LED channels, and the power supplier includes: a rectifying and smoothing
unit rectifying and smoothing commercial power; a power factor correction
unit adjusting a phase difference between voltage and current of the
rectified power from the rectifying and smoothing unit; a switching unit
switching power of which power factor is corrected from the power factor
correction unit according to the switching control signal; a transformer
having at least one primary winding that receives the switched power from
the switching unit and at least one secondary winding that is insulated
from the at least one primary winding and receives the power from the at
least one primary winding by forming a previously set turn ratio; and a
current balance unit having at least one current balance unit element
that maintains current balance in the driving power supplied to each of
the first and second LED channels.

14. The light emitting diode driver of claim 13, wherein the at least one
current balance unit element includes: a current balance capacitor
connected to one end of the secondary winding to maintain current balance
between the driving power transferred to each of the first and second LED
channels, according to a charge balance law; a first diode connected
between the other end of the secondary winding and the first LED channel
to rectify the driving power; a second diode connected between the
current balance capacitor and the second LED channel to rectify the
driving power; a first stabilization capacitor connected to the first LED
channel in parallel to stabilize the driving power; and a second
stabilization capacitor connected to the second LED channel in parallel
to stabilize the driving power.

15. The light emitting diode driver of claim 13, wherein the secondary
winding is separated into a previously set turn number based on a center
tap, the first LED channel and the second LED channel are connected in
series, and the at least one balance unit element includes: a current
balance capacitor connected to the center tap of the secondary winding
and connected to a connection point of the first and second LED channels
to maintain the current balance between the driving power transferred to
the first and second LSD channels, respectively; a first diode connected
between one end of the secondary winding and the first LED channel to
rectify the driving power; a second diode connected between the other end
of the secondary winding and the second LED channel to rectify the
driving power; a first stabilization capacitor connected to the first LED
channel in parallel to stabilize the driving power; and a second
stabilization capacitor connected to the second LED channel in parallel
to stabilize the driving power.

16. The light, emitting diode driver of claim 14, wherein the transformer
includes a plurality of secondary windings, the secondary windings
respectively connected to a plurality of LED channel blocks, and
supplying the driving power to a corresponding LED channel block, and the
current balance unit including the current balance unit element provided
in plural to maintain the driving power from the plurality of secondary
windings in a current balance state and supply the current balanced
driving power to the first LED channel and the second LED channel of a
corresponding LED channel block.

17. The light emitting diode driver of claim 16, wherein the transformer
includes a plurality of primary windings respectively corresponding to
the plurality of secondary windings.

18. The light emitting diode driver of claim 15, wherein the transformer
includes a plurality of secondary windings, the secondary windings
respectively connected to a plurality of LED channel blocks, and
supplying the driving power to a corresponding LED channel block, and the
current balance unit including the current balance unit element provided
in plural to maintain the driving power from the plurality of secondary
windings in a current balance state and supply the current balanced
driving power to the first LED channel and the second LED channel of a
corresponding LED channel block.

19. The light emitting diode driver of claim 18, wherein the transformer
includes a plurality of primary windings respectively corresponding to
the plurality of secondary windings.

20. A light emitting diode driver, comprising: a rectifying and smoothing
unit rectifying and smoothing commercial power; a power factor correction
unit adjusting a phase difference between voltage and current of the
rectified power from the rectifying and smoothing unit; a switching unit
switching the power of which power factor is corrected from the power
factor correction unit according to the switching control signal; a
transformer having at least one primary winding that receives the
switched power from the switching unit and at least one secondary winding
that is electrically insulated from at least one primary winding and
receives the power from the at least one primary winding by forming a
previously set turn ratio; a current balance unit having at least one
current balance unit element that maintains current balance in a driving
power supplied to each of first and second LED channels of at least one
LED channel block having the first and second LED channels; a switch unit
connected between the at least one LED channel and a ground to switch a
supply or an interruption of the driving power to the at least one LSD
channel; and a controller detecting a state of the driving power supplied
to the at least one LED channel to control the switching of the switch
unit and generating the switching control signal according to the state
of the detected driving power and to transfer the generated switching
control signal to the transfer unit; and a transferring unit having a
pulse transformer including a first winding that receives the switching
control signal controlling the switching of the power supplier from the
controller and a second winding that is electrically insulated from the
first winding and receives the switching control signal input to the
first winding to transfer the received switching control signal to the
switching unit.

21. The light emitting diode driver of claim 20, wherein the controller
includes: a current generator generating current set according to the
state of the detected driving power; a clock generator generating a clock
signal having a period set according to the current generated by the
current generator; a dead time generator generating a dead time of the
clock signal generated by the clock generator according to the current
generated by the current generator; a gate driver processing the clock
signal having the dead time generated by the dead time generator to
control the switching of the power supplier and transferring the
processed clock signal to the transfer unit; a dimming unit controlling
the switching of the switch unit according to the state of the detected
driving power to control luminance of the at least one LED channel; and a
protection unit interrupting an operation of the gate driver when the
state of the detected driving power corresponds to a previously set
abnormal operation.

22. The light emitting diode driver of claim 21, wherein the dimming unit
includes: a calculator receiving the state of the detected driving power
as a detection signal to calculate a current control signal transferred
to the current generator when a pulse width modulation (PWM) signal
turning-on and turning-off the switch unit is a high signal; and a buffer
unit controlling a voltage level of the detection signal to a previously
set voltage level when the PWM signal is a low signal.

23. The light emitting diode driver of claim 22, wherein the at least one
current balance unit element includes: a current balance capacitor
maintaining current balance between the driving power transferred to each
of the first and second LED channels according to a charge balance law;
first and second diodes connected between the first LED channel and a
ground in series to rectify the driving power; third and fourth diodes
connected between the second LED channel and the ground in series to
rectify the driving power; a first stabilization capacitor connected to
the first and second diodes in parallel to stabilize the driving power
supplied to the first LED channel; and a second stabilization capacitor
connected to the third and fourth diodes in parallel to stabilize the
driving power supplied to the second LED channel

24. The light emitting diode driver of claim 22, wherein the at least one
current balance unit element includes: a current balance capacitor
connected to one end of the secondary winding to maintain current balance
between the driving power transferred to each of the first and second LED
channels, according to a charge balance law; a first diode connected
between the other end of the secondary winding and the first LED channel
to rectify the driving power; a second diode connected between the
current balance capacitor and the second LED channel to rectify the
driving power; a first stabilization capacitor connected to the first LED
channel in parallel to stabilize the driving power; and a second
stabilization capacitor connected to the second LED channel in parallel
to stabilize the driving power.

25. The light emitting diode driver of claim 22, wherein the secondary
winding is separated into a previously set turn number based on a center
tap, the first LED channel and the second LED channel are connected in
series, and the at least one balance unit element includes: a current
balance capacitor connected to the center tap of the secondary winding
and connected to a connection point of the first and second LED channels
to maintain the current balance between the driving power transferred to
the first and second LED channels, respectively; a first diode connected
between one end of the secondary winding and the first LED channel to
rectify the driving power; a second diode connected between the other end
of the secondary winding and the second LED channel to rectify the
driving power; a first stabilization capacitor connected to the first LED
channel in parallel to stabilize the driving power; and a second
stabilization capacitor connected to the second LED channel in parallel
to stabilize the driving power.

26. The light emitting diode driver of claim 23, wherein the transformer
includes a plurality of secondary windings, the secondary windings
respectively connected to a plurality of LED channel blocks, and
supplying the driving power to a corresponding LED channel block, and the
current balance unit including the current balance unit element provided
in plural to maintain the driving power from the plurality of secondary
windings in a current balance state and supply the current balanced
driving power to the first LED channel and the second LED channel of a
corresponding LED channel block.

27. The light emitting diode driver of claim 26, wherein the transformer
includes a plurality of primary windings respectively corresponding to
the plurality of secondary windings.

28. The light emitting diode driver of claim 25, wherein the transformer
includes a plurality of secondary windings, the secondary windings
respectively connected to a plurality of LED channel blocks, and
supplying the driving power to a corresponding LED channel block, and the
current balance unit including the current balance unit element provided
in plural to maintain the driving power from the plurality of secondary
windings in a current balance state and supply the current balanced
driving power to the first LED channel and the second LED channel of a
corresponding LED channel block.

29. The light emitting diode driver of claim 28, wherein the transformer
includes a plurality of primary windings respectively corresponding to
the plurality of secondary windings.

Description:

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the priority of Korean Patent Application
No. 10-2010-0126900 filed on Dec. 13, 2010, in the Korean Intellectual
Property Office, the disclosure of which is incorporated herein, by
reference,

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a light emitting diode driver
capable of driving a light emitting diode by converting a commercial
power supply into a driving power supply.

[0004] 2. Description of the Related Art

[0005] Recently, in the area of displays, a display device mainly using a
cathode ray tube (CRT) has been replaced with a high-resolution large
flat panel display (FPD) device, reflecting users' demands.

[0006] In particular, in the case of a large display device, demand for a
liquid crystal display (LCD) has been remarkably increased due to the
advantages of slimness and lightness thereof, which will solidify an
LCD's leading position in terms of price and marketability in the future.

[0007] Meanwhile, in the case of an existing liquid crystal display
device, a cold cathode fluorescent lamp (CCFL) has mainly been used as a
backlight light source. However, the use of a light emitting diode (LED)
is gradually being increased due to various advantages such as power
consumption, lifespan, environmental-friendliness, efficiency, or the
like.

[0008] In order to drive the light emitting diode, a power supply circuit
converting commercial alternating current (AC) power into direct current
(DC) power and a driving circuit controlling a supply of DC power to the
light emitting diode have generally been used. The power supply circuit
may be divided into a primary side and a secondary side, based on a
transformer, in order to enhance an insulating function. The primary side
is configured as a circuit rectifying and smoothing the commercial AC
power to switch a power supply and a secondary side is configured as a
circuit rectifying power transformed by the transformer and controlling
the supply of the rectified power to a load. Generally, the primary side
is provided with a power switching control circuit and a secondary side
is provided with the driving circuit. In this case, in order to smoothly
control the switching of a power supply, the power state supplied to the
light emitting diode may be fedback to a power switching control circuit
to control the switching based on the fedback power state. To this end, a
plurality of photo couplers including an insulating function to transfer
a feedback current, have mainly been used. However, since the photo
coupler is an optical device, signal transfer characteristics depend on
photons, used time, and junction temperature, such that it is difficult
to design a circuit and manufacturing costs may be increased due to the
use of the photo coupler.

SUMMARY OF THE INVENTION

[0009] An aspect of the present invention provides a light, emitting diode
driver that integrates a light emitting diode control function and a
power switching control function at a secondary side insulated from a
primary side in a power supply circuit to thereby control power switching
of the primary side.

[0010] According to an aspect of the present invention, there is provided
a light emitting diode driver, including: a power supplier including a
primary side and a secondary side electrically insulated from each other,
switching input power at the primary side and converting the switched
power into driving power having a previously set voltage level at the
secondary side, and supplying the driving power to at least one light
emitting diode (LED) channel; a driver controlling a supply and an
interruption of the driving power to the at least one LED channel from
the power supplier to drive the at least one LED channel and controlling
switching of the power supplier according to a state of the driving power
supplied to the at least one LED channel; and a transfer unit
transferring a switching control signal controlling the switching of the
power supplier from the driver to the primary side of the power supplier
from the secondary side thereof.

[0011] The driver may include a switching unit connected between the at
least one LED channel and a ground to switch the supply or interruption
of the driving power to the at least one LED channel; and a controller
detecting the state of the driving power supplied to the at least one LED
channel to control the switching of the switching unit and generating the
switching control signal according to the state of the detected driving
power and to transfer the generated switching control signal to the
transfer unit.

[0012] The controller may include: a current generator generating current
set according to the state of the detected driving power; a clock
generator generating a clock signal having a period set according to the
current generated by the current generator; a dead time generator
generating a dead time of the clock signal generated by the clock
generator according to the current generated by the current generator; a
gate driver processing the clock signal having the dead time generated by
the dead time generator to control the switching of the power supplier
and transferring the processed clock signal to the transfer unit; a
dimming unit controlling the switching of the switching unit according to
the state of the detected driving power to control luminance of the at
least one LED channel; and a protection unit interrupting an operation of
the gate driver when the state of the detected driving power corresponds
to a previously set abnormal operation.

[0013] The dimming unit may include: a calculator receiving the state of
the detected driving power as a detection signal to calculate a current
control signal transferred to the current generator when a pulse width
modulation (PWM) signal turning-on and turning-off the switching unit is
a high signal; and a buffer unit, controlling a voltage level of the
detection signal to a previously set voltage level when the PWM signal is
a low signal. The transfer unit may be a pulse transformer including a
first winding that receives the switching control signal from the gate
driver and a second winding that is electrically insulated from the first
winding and receives the switching control signal input to the first
winding to transfer the received switching control signal to the power
supplier.

[0014] The light emitting diode driver may further include a rectifier
rectifying the driving power from the power supplier and supplying the
rectified driving power to the at least one LED channel.

[0015] The power supplier may supply the driving power to each of first
and second LED channels of at least one LED channel block having the
first and second LED channels.

[0016] The light emitting diode driver may further include a current
balance unit having at least one current balance unit element that
maintains current balance in the driving power supplied to each of the
first and second LED channels.

[0017] The at least one current balance unit element may include; a
current balance capacitor maintaining current balance between the driving
power transferred to each of the first and second LED channels according
to a charge balance law; first and second diodes connected between the
first LED channel and a ground in series to rectify the driving power;
third and fourth diodes connected between the second LED channel and the
ground in series to rectify the driving power; a first stabilization
capacitor connected to the first, and second, diodes in parallel to
stabilize the driving power supplied to the first LED channel; and a
second stabilization capacitor connected to the third and fourth diodes
in parallel, to stabilize the driving power supplied to the second LED
channel. The at least one current balance unit element may include; a
current balance capacitor connected to one end of the secondary winding
to maintain current balance between the driving power transferred to each
of the first and second LED channels, according to a charge balance law;
a first diode connected between the other end of the secondary winding
and the first LED channel to rectify the driving power; a second diode
connected between the current balance capacitor and the second LED
channel to rectify the driving power; a first stabilization capacitor
connected to the first LED channel in parallel to stabilize the driving
power; and a second stabilization capacitor connected to the second LED
channel in parallel to stabilize the driving power. The secondary winding
is separated into a previously set turn number based on a center rap, the
first LED channel and the second LED channel are connected in series, and
the at least one balance unit element includes: a current balance
capacitor connected to the center tap of the secondary winding and
connected to a connection point of the first and second LED channels to
maintain the current balance between the driving power transferred to the
first and second LED channels, respectively; a first diode connected
between one end of the secondary winding and the first LED channel to
rectify the driving power; a second diode connected between, the other
end of the secondary winding and the second LED channel to rectify the
driving power; a first stabilization capacitor connected to the first LED
channel in parallel to stabilize the driving power; and a second
stabilization capacitor connected, to the second LED channel in parallel,
to stabilize the driving power.

[0018] The power supplier may include; a rectifying and smoothing unit
rectifying and smoothing commercial power; a power factor correction unit
adjusting a phase difference between voltage and current of the rectified
power from the rectifying and smoothing unit; a switching unit switching
power of which power factor is corrected from the power factor correction
unit according to the switching control signal; and a transformer having
at least one primary winding that receives the switched power from the
switching unit and at least one secondary winding that is insulated from
the at least one primary winding and receives the power from the at least
one primary winding by forming a previously set turn ratio.

[0019] The transformer may include a plurality of secondary windings, the
secondary windings respectively connected to a plurality of LED channel
blocks, and supplying the driving power to a corresponding LED channel
block, and the current balance unit including the current balance unit
element provided in plural, to maintain the driving power from the
plurality of secondary windings in a current balance state and supply the
current balanced driving power to the first LED channel and the second
LED channel of a corresponding LED channel block.

[0020] The transformer may include a plurality of primary windings
respectively corresponding to the plurality of secondary windings.

[0021] The above and other aspects, features and other advantages of the
present, invention will be more clearly understood from the following
detailed, description taken in conjunction with the accompanying
drawings, in which:

[0022]FIG. 1 is a schematic configuration diagram of a light emitting
diode driver according to a first exemplary embodiment of the present
invention;

[0023] FIG. 2 is a schematic configuration diagram of a light emitting
diode driver according to a second exemplary embodiment of the present
invention;

[0024]FIG. 3 is a schematic configuration diagram of a light emitting
diode driver according to a third exemplary embodiment of the present
invention;

[0025]FIG. 4 is a schematic configuration diagram of a light emitting
diode driver according to a fourth exemplary embodiment of the present
invention;

[0026] FIGS. 5A to 5C are schematic configuration diagrams of examples of
a switching unit used in the light emitting diode driver of the exemplary
embodiment of the present invention;

[0027] FIG. 6 is a schematic configuration diagram of a controller used in
the used in the light emitting diode driver of the exemplary embodiment
of the present invention;

[0028]FIG. 7 is a partially enlarged diagram of the controller used in
the used in the light emitting diode driver of the exemplary embodiment
of the present invention;

[0029] FIGS. 8A and 9A are graphs showing electrical characteristics of a
general light emitting diode driver and

[0030] FIGS. 8B and 9B are graphs showing electrical characteristics of
the light emitting diode driver according to the exemplary embodiment of
the present invention,

[0031]FIG. 10 is a signal waveform graph of main components of the light
emitting diode driver according to the exemplary embodiment of the
present invention;

[0032] FIGS. 11A and 11B are schematic configuration diagrams of examples
of a current balance unit used in the light emitting diode driver of the
exemplary embodiment of the present invention; and

[0033] FIGS. 12A and 12B are a current flow diagram showing an operation
of a current balance unit used in the light emitting diode driver of the
exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0034] Exemplary embodiments of the present invention will now be
described in detail with reference to the accompanying drawings.

[0035]FIG. 1 is a schematic configuration diagram of a light emitting
diode driver according to a first exemplary embodiment of the present
invention.

[0036] Referring to FIG. 1, a light emitting diode driver 100 according to
a first exemplary embodiment of the present invention may be configured
to include a power supplier 110, a driver 120, a transfer unit 130, and a
rectifier 140.

[0037] The power supplier 110 may be configured to include a rectifying
and smoothing unit 111 receiving commercial AC power, and rectifying and
smoothing the received commercial AC power, a power factor correction
unit 112 adjusting a phase difference between voltage and current of
power rectified in the rectifying and smoothing unit ill, and correcting
power factor, a switching unit 113 switching power of which the power
factor is corrected in the power factor correction unit 112, and a
transformer 114 changing a voltage level of power switched by the
switching unit 113. Although not shown in FIG. 1, the power supplier 110
may further include an electromagnetic interference (EMI) filter in order
to remove EMI.

[0038] The switching unit 113 may be configured to include an LLC
resonance inverter connected to two switches alternately switching the
power of which the power factor is corrected in the power factor
correction unit 113 and having leakage inductance L1kg and resonance
capacitor C. However, as shown in FIGS. 5A to 5C, examples of the
switching unit 113 used in the light emitting diode driver 100 according
to the first exemplary embodiment of the present invention may be
configured to include a half bridge inverter (FIG. 5A), a full-bridge
inverter (FIG. 5B), or a push-pull inverter (FIG. 5C), or the like.

[0039] The transformer 114 may be configured to include at least one
primary winding Np and at least one secondary winding Ns. The primary
winding Np receives power switched by the switching unit 113 and the
secondary winding Ns is electrically insulated, from the primary winding
Np and receives the power inputted to the primary winding Np according to
a preset turn ratio with the primary winding Np to transform the voltage
level. The transformed power may be transferred to at least one light
emitting diode channel LED in which a plurality of light emitting diodes
are connected in series.

[0040] The driver 120 may include a switching unit 121 and a controller
122.

[0041] The switching unit 121 is connected to the light emitting diode
channel LED to be turned-on and turned-off according to a dimming signal,
such that the driving power is supplied or is not supplied to the light
emitting diode channel LED.

[0042] The controller 122 controls the turn-on and turn-off of the
switching unit 121 according to the state of the power supplied to the
light emitting diode channel LED and controls the switching of the
switching unit 113, thereby controlling the voltage level or the current
level of the power supplied to the light emitting diode channel LED.

[0043] The transfer unit 130 transfers the switching control signal from
the controller 122 to the switching unit 113 in a magnetic induction
method. To this end, the transfer unit 130 may be configured to include a
pulse transformer including a first winding N1 and a second winding N2.
The first winding N1 and the second winding N2 are electrically insulated
from each other. The first winding N1 receives the switching control
signal from the controller 122 and the second winding N2 may transfer the
switching control signal S magnetically induced from the first winding N1
electrically insulated from the second winding N2.

[0044] The rectifying unit 140 may be configured to include a capacitor
Cb1, first to fourth diodes D1 to D4, and a stabilization capacitor Co1
and may rectify and stabilize power from the secondary winding Ns of the
transformer 114 to supply the driving power to the light emitting diode
channel LED. As shown, one end of the capacitor Cb1 may be connected to
one end of the secondary winding Ns, first and second diodes D1 and D2
may be connected to each other in series, and the other end of the
capacitor Cb1 may be connected to a connection point of the first and
second diodes D1 and D2. Third and fourth diodes D3 and D4 may be
connected to each other in series and may be connected to the first and
second diodes D1 and D2 in parallel, the other end of the secondary
winding Ns may be connected to the connection point of the third and
fourth diodes D3 and D4, and the stabilization capacitor Co1 may be
connected to the third and fourth diodes D3 and D4 in parallel.

[0045] As described above, the rectifying and smoothing unit 111, the
power factor correction unit 112, the switching unit, the primary winding
Np of the transformer 114, and the secondary winding N2 of the transfer
unit 130 may be formed at the primary side and the driver 120, the
rectifier 140, the secondary winding Ns of the transformer 114, and the
first winding N1 of the transfer unit 130 may be formed, at the secondary
side. Therefore, a function of controlling the switching of the primary
side and a function of driving the light emitting diode of the secondary
side may be formed to be integrated at the secondary side.

[0046] FIG. 2 is a schematic configuration diagram of a light emitting
diode driver according to a second exemplary embodiment of the present
invention;

[0047] Referring to FIGS. 1 and 2, a light emitting diode driver 200
according to a second exemplary embodiment of the present invention may
supply the driving power to at least two light emitting diode channels
LED1 and LED2. Therefore, the light emitting diode driver 200 according
to the second exemplary embodiment of the present invention, may be
configured to include a current balance unit 240 unlike the rectifier of
FIG. 1.

[0048] The current balance unit 240 may be configured to include the
current balance capacitor Cb1, the first to fourth diodes D1 to D4, and
the first and second stabilization capacitors Co1 and Co2. As shown, one
end of the current balance capacitor Cb1 may be connected to one end of
the secondary winding Ns, first and second diodes D1 and D2 may be
connected to each other in series, the other end of the capacitor Cb1 may
be connected to the connection point of the first and second diodes D1
and D2, and the second stabilization capacitor Co2 may be connected to
the first and second diodes D1 and D2 in parallel. The third and fourth
diodes D3 and D4 may be connected to each other in series, the other end
of the secondary winding Ns may be connected to the connection point of
the third and fourth diodes D3 and D4, and the first stabilization
capacitor Col may be connected to the third and fourth diodes D3 and D4
in parallel.

[0049] The current balance capacitor Cb1 may maintain the current balance
between the driving power supplied to the first light emitting diode
channel LED1 and the driving power supplied to the second light emitting
diode channel LED2 according to a charge average principle. The detailed
description thereof will be described in detail with reference to FIGS.
12A and 12B.

[0050] Meanwhile, the configuration and function of the rectifying and
smoothing unit 211, the power factor correction unit 212, the switching
unit 213, and the transformer 214 in the power supplier 210, the driver
220 having the controller 222, and the transfer unit 230 are the same as
the description of FIG. 1 and therefore, the detailed description thereof
will be omitted.

[0051]FIG. 3 is a schematic configuration diagram of a light emitting
diode driver according to a third exemplary embodiment of the present
invention.

[0052] Referring to FIG. 3, in a light emitting diode driver 300 according
to a third exemplary embodiment of the present invention, a transformer
314 includes a plurality of secondary winding NS1 to NSN, a
current balance unit 340 includes a plurality of current balance unit
elements 341 to 34N, and each of the plurality of current balance unit
elements 341 to 34N may be electrically connected a plurality of
corresponding secondary windings NS1 to NSN. Each of the
plurality of current balance unit elements 341 to 34N may be the same as
the configuration of the current balance unit 240 shown in FIG. 2 and the
detailed description thereof will be omitted. In addition, the resonance
capacitance C may be different from the positions shown in FIGS. 1 and 2,
but does not affect the LLC resonance and the description of the leakage
inductance L1kg will be omitted.

[0053] Meanwhile, the configuration and function of the rectifying and
smoothing unit 311, the power factor correction unit 312, and the
switching unit 313 in the power supplier 310, the driver 320 having the
switching unit 321 and the controller 322, and the transfer unit 330 are
the same as the description of FIG. 1 and therefore, the detailed
description thereof will be omitted.

[0054]FIG. 4 is a schematic configuration diagram of a light emitting
diode driver according to a fourth exemplary embodiment of the present
invention.

[0055] Referring to FIG. 4, in a light emitting diode driver 400 according
to the fourth exemplary embodiment of the present invention, a
transformer 414 includes a plurality of primary windings NP1 to
NPN and a plurality of secondary windings NS1 to NSN,
wherein the plurality of primary windings NP1 to NPN one-to-one
corresponds to the plurality of secondary windings NS1 to NSN.
The current balance unit 440 includes a plurality of current balance unit
elements 441 to 44N and each of the plurality of current balance unit
elements 441 to 44N may be electrically connected to the plurality of
corresponding secondary windings NS1 to NSN. Each of the
plurality of current balance unit elements 441 to 44N may be the same as
the configuration of the current balance unit 240 shown in FIG. 2 and the
detailed description thereof will be omitted.

[0056] Meanwhile, the configuration and function of the rectifying and
smoothing unit 411, the power factor correction unit 412, and the
switching unit 413 in the power supplier 410, the driver 420 having the
switching unit 421 and the controller 422, and the transfer unit 430 are
the same as the description of FIG. 1 and therefore, the detailed
description thereof will be omitted.

[0057] FIG. 6 is a schematic configuration diagram of a controller used in
the used in the light emitting diode driver of the exemplary embodiment
of the present invention and FIG. 7 is a partially enlarged diagram of
the controller used in the used in the light emitting diode driver of the
exemplary embodiment of the present invention.

[0058] Referring to FIG. 6, the controller used in the light emitting
diode driver according to the exemplary embodiment of the present
invention may be commonly used in the light emitting diode derivers 100,
200, 300, and 400 according to the exemplary embodiments of the present
invention and therefore, the controller 122 of FIG. 1 will be described.

[0059] The controller 122 may be configured to include a current generator
122a, a clock generator 122b, a dead time generator 122c, a gate driver
122d, a dimming unit 1223, and a protecting unit 122f.

[0060] The current generator 122a may generate the current having a level
set according the state of the driving power supplied to the light
emitting diode channel LED1 and the clock generator 122b may generate the
clock signal having a period set according to the current generated by
the current generator 122a.

[0061] The dead time generator 122c generates a dead time for controlling
the switching of the switching unit 113 based on the current level
generated by the current generator 122a and the clock signal generated by
the clock generator 122b and the gate driver 122d generates the switching
control signal having the dead time generated by the dead time generator
122c based on a pulse width modulation (PWM) signal from the outside,
which may be transferred to the switching unit 113 through the transfer
unit 130.

[0062] The dimming unit 122e may supply the switching signal SW
controlling the supply and interruption of the driving power to the light
emitting diode channel LED1 based on the PWM signal supplied to the gate
driver 122d or the analog dimming signal ADIM from the outside. To this
end, the dimming unit 122e may receive the driving power supplied to the
light emitting diode channel LED1, which is detected by a detection
resistor RSEN, as first and second feedback signals FB1 and FB2
through resistors R1 and R2.

[0063] In addition, the dimming unit 122e may receive the driving power
supplied to the light emitting diode channel LED1 as an error signal ER0
by the resistor R2 and an RC network. The above-mentioned error signal.
ER0 is transferred to the current generator 122a to be associated with
the current generation.

[0064] The protection unit 122f determines the normal or abnormal
operation according to the voltage and current states SEP and OLP of the
power supplied to the light emitting diode channel LED1, thereby stopping
the operations of the current generator 122a and the gate driver 122d at
the time of the abnormal operation.

[0065] Meanwhile, referring to FIG. 7, the dimming unit 122e may include a
calculator 122e-1 and a buffer unit 122e-2, and the calculator 122e-1 may
receive a feedback signal FB1 having the current level of the driving
power supplied to the light emitting diode channel LED1 by the voltage
level VSEN of the driving power supplied to the light emitting diode
channel LED1 detected by the detection resistance RSEN.

[0066] The calculator 123e-1 varies a frequency according to the level of
the feedback signal FB1 to control pulse frequency modulation (PFM).

[0067] Describing the operation, when the PWM signal from the outside is
high, the switch M1 of the switching unit 121 is in the turned-on state
to transfer the feedback signal FB1 to the calculator 122e-1, thereby
controlling the current (RT) generation of the current generator 122a. In
this case, the switch Q1 of the buffer unit 122e-2 is turned-off such
that the operation is not performed.

[0068] When the PWM signal is low, the switch Ml of the switching unit 121
Is in the turned-off state and the switch Q1 of the buffer unit 122e-2 is
turned-on to maintain the voltage level of the error signal ER0 as the
voltage level of the analog dimming signal ADIM, thereby such that the
voltage level of the error signal ER0 may be set through the analog
dimming signal ADIM even when the PWM signal is low, similar to the level
of the feedback signal FB1.

[0069] FIGS. 8A and 9A are graphs showing electrical characteristics of a
general light emitting diode driver and FIGS. 8B and 9B are graphs
showing electrical characteristics of the light emitting diode driver
according to the exemplary embodiment of the present invention.

[0070] Meanwhile, when the feedback level signal is transferred, the
phenomenon that the current level rises as in identification sign A of
FIG. 8A due to the external resistance and the capacitor component of the
calculator 122e-1 occurs.

[0071] However, in the dimming unit 122e of the exemplary embodiment of
the present invention, even when the PWM signal is low, the voltage level
of the error signal ER0 is constantly maintained as in a period of a high
signal of the PWM signal, such that the rising time of the current
ILED flowing in the light emitting diode channel LED1 can be
shortened as shown in FIG. 8B even when the PWM signal is dimmed-on in
the low level, the dimming-off.

[0072] In the LLC power conversion manner, the switching control signal
Sis operated at a low frequency at the time of no-load to increase the
gain of the output voltage. As a result, when the PWM signal is low, the
output voltage VOUT is increased. The increase in the output voltage
leads to instantaneously increase the current (LED current) flowing in
the light emitting diode channel LED1 as in identification sign B of FIG.
9A when the PWM signal is high. As a result, in the exemplary embodiment
of the present invention, when the PWM signal is low, the output of the
switching control signal is turned-off to maintain the output voltage
VOUT, thereby stably maintaining the current (LED current) level
flowing in the light emitting diode channel LED1 as shown in FIG. 9B.

[0073] In addition, the controller 122 is formed at the secondary side,
such that the power control circuit is generally formed at the primary
side to exclude the use of the photo coupler for transferring the power
state generated at the secondary side to the primary side.

[0074]FIG. 10 is a signal waveform graph of main, components of the light
emitting diode driver according to the exemplary embodiment of the
present invention.

[0075] When any abnormal operation is applied at a normal operation as in
identification sign (1), (2), and (3), it can be appreciated from FIG. 10
that the protection operation may be easily made. That is, as in
identification sign (1), the voltage of the switch M1 of the switching
unit 121 falls to a predetermined voltage or less to charge the capacitor
of an SDT when an over LED protection (OLP) voltage level is low, such
that it can be appreciated that the protection function may be operated
when the charged voltage level is a predetermined level or more of about
0.7V. In identification signal (2), when the drain voltage of the switch
M1 is a predetermined voltage or more of about 4V as the case in which
the channel is short-circuited (short LED protect ion (SLP)), a
latch-shutdown is immediately made and when the drain voltage of the
switch M1 is 3V or more, the capacitor for shut-down time (SDT) is
charged, such that it can be appreciated that the protection function is
operated (short LED protection (SLP)) when the drain voltage is a
predetermined voltage or more. In identification signal (3), when
overcurrent occurs at the primary side, the output of the switching
control signal S stops when the over current protection (OCP) voltage is
a predetermined voltage level of about 2V, such that it can be
appreciated that the protection function is operated.

[0076] Meanwhile, FIGS. 11A and 11B are schematic configuration diagrams
of examples of a current balance unit used in the light emitting diode
driver of the exemplary embodiment of the present invention;

[0077] Referring to FIG. 11A, a first current balance unit element may be
configured to include a first diode D1 and a second diode D2, the first
current balance capacitor Cb1 is electrically connected between one end
of a first secondary winding NS1 and an anode of the second diode D2, an
anode of the first diode D1 is electrically connected to the other end of
the first secondary winding NS1, a cathode of the first diode D1 is
electrically connected to one end of the first stabilization capacitor
Co1 and one end of the first light emitting diode channel LED1, the anode
of the second diode D2 is electrically connected to the other end of the
first stabilization capacitor Co1 and the first light emitting diode
channel LED1 together with the first current balance capacitor Cb1, the
cathode of the second diode D2 is electrically connected to one end of
the second stabilization capacitor Co2 and one end of the second light
emitting diode channel LED2, and the other end of the second
stabilization capacitor Co2 and the other end of the second light
emitting diode channel LED2 may be electrically connected to the other
end of the first secondary winding NS1. As described above, only the
first current balance unit element is described, but the second current
balance unit including the second current balance capacitor Cb2, the
third and fourth diodes D3 and D4, and the third and fourth stabilization
capacitors Co3 and Co4 may have the same configuration as the first
current balance unit element. The current balance unit element may be
provided in plural.

[0078] Referring to FIG. 11B, the first current balance unit element
includes the first diode D1 and the second diode D2, the first secondary
winding NS1 is separately wound to include a center tap, the first
current balance capacitor Cb1 is connected between the center tap of the
first secondary winding NS1 and the ground, the anode of the first diode
D1 is electrically connected, to one end of the first secondary winding
NS1, the cathode of the first diode D1 is electrically connected to
one end of the first stabilization capacitor Co1 and one end of the first
light emitting diode channel LED1, the anode of the second diode D2 is
electrically connected to the other end of the first secondary winding
NS1, the cathode of the second diode D2 is electrically connected to
one end of the second stabilization capacitor Co2 and one end of the
second light emitting diode channel LED2, and the other end of the first
and second stabilization capacitors Co1 and Co2 and the other end of the
first and second light emitting diodes LED1 and LED2 may be ground.
Similarly, only the first current balance unit element is described
above, but the second current balance unit element including the second
current balance capacitor Cb2, the third and fourth diodes D3 and D4, and
the third and fourth, stabilization capacitors Co3 and Co4 may have the
same configuration as the first current balance unit element. The current
balance unit element may be provided in plural.

[0079] FIGS. 12A and 12B are a current flow diagram showing an operation
of the current balance unit used in the light emitting diode driver of
the exemplary embodiment of the present invention.

[0080] The current flowing in the primary winding NP according to the
switching of the switching unit 113 alternately flows forward (FIG. 12A)
and reverse (FIG. 12B). In this case, in order to equalize the
electromagnetic coupling between the first and second secondary windings
NS1 and NS2 and the primary winding NP, when the tarn ratio
between the first and second secondary windings NS1 and NS2 are
the same, the positive power current Isec1_P and Isec2_P may approximate
to each other in the case of the forward.

Isec1--P≈Isec2--P (*P Positive) [Equation 1]

[0081] Similarly, in the case of the reverse, the current Isec1_N and
Isec2_N of the negative power of the first and second secondary windings
NS1 and NS2 approximates to each other as the following
Equation 2.

Isec1--N≈Isec2--N (*N: Negative) [Equation 2]

[0082] In this case, each rectifier may include one of the current balance
capacitors Cb1 and Cb2. As shown in FIGS. 12A and 12B, the forward and
reverse current conduction paths are formed and the power supplied to the
first and third light emitting diode channels LED1 and LED3 and the
second and fourth light emitting diode channels LED2 and LED4 according
to the charge balance law of the current balance capacitors Cb1 and Cb2
may approximate to each other as the following Equations 3 and 4 (charge
balance principle is a known art and the detailed description thereof
will be omitted)

Isec1,2_P≈Isec1,2_N [Equation 3]

Isec1_P≈Isec2_P≈Isec1_N≧Isec2_N [equation 4]

[0083] That is, the current of the driving power supply supplied to the
first to fourth light emitting diode channels LED1 to LED4 may be
constantly maintained.

[0084] As various exemplary embodiments of the above-mentioned
configuration, when a single transformer includes N secondary windings of
which the turn number is the same, the current balance of the driving
power supplied to at least 2N light emitting diode lamps is maintained
according to the charge balance law of N current balance capacitors
provided corresponding to each secondary winding, such that a constant
current may flow in each, light emitting diode lamp.

[0085] As set forth, above, the exemplary embodiment of the present
invention integrates the switching control circuit formed at the primary
side and the light emitting diode control circuit formed at the secondary
side, thereby reducing the manufacturing costs without using the photo
coupler.

[0086] As set forth above, the exemplary embodiment of the present
invention integrates the light emitting diode control function and the
power switching control function at the secondary side to control the
power switching of the primary side, thereby reducing the manufacturing
costs, facilitating the circuit, design, preventing the current rising
delay, and suppressing the current spike components.

[0087] While the present invention has been shown and described in
connection with one exemplary embodiments, it will be apparent to those
skilled in the art that modifications and variations can be made without
departing from the spirit and scope of the invention as defined by the
appended claims.

Patent applications by Jae Shin Lee, Anyang KR

Patent applications by Jeong In Cheon, Seoul KR

Patent applications by Samsung Electro-Mechanics Co., Ltd.

Patent applications in class Periodic switch in the primary circuit of the supply transformer

Patent applications in all subclasses Periodic switch in the primary circuit of the supply transformer